CMOS active bandpass filter using compacted synthetic quasi-TEM lines at C-band

This paper presents a fully monolithic transmission-line-based active bandpass filter (BPF) fabricated in a 0.18-μm standard complementary metal-oxide-semiconductor (CMOS) technology. The half-wavelength resonators are realized by synthetic quasi-TEM complementary conducting-strip transmission lines (CCS TLs). To lower the insertion loss of the BPF, the differential nMOS cross-coupled pairs are combined with the parallel resonators. Besides, the active devices and CCS TLs are vertically integrated on the standard CMOS substrate. The Q-enhanced resonator, which is comprised of a CCS TL and an nMOS cross-coupled pair, is theoretically investigated. Simulation results indicate that the Q factor of the resonator can be increased from 3.4 to 84.0 at 6.53 GHz. Additionally, the prototype of the second-order BPF occupies an area of 1230 μm × 880 μm, and the measured results demonstrate that the center frequency is 6.02 GHz with a bandwidth of 1.14 GHz. The P1dB and insertion loss are -15.2 dBm and 2.2 dB, respectively, when the BPF consumes 3.0 mA from a 1.8-V supply. A two-port noisy network is also reported to examine the noise figure (NF) of the proposed BPF. Theoretical results reveal that the NF is 11.38 dB at 6.0 GHz, with a difference of less than 7.2% among the measured data.